It depends on what you're trying to do. The fact that you say "strip" makes me think you're doing like a 4 panel thing... in which case sometimes you only really need 2 or 3 characters for the whole strip. Think of how many comic strips just have two characters talking to each other with an occasional third character there if the joke calls for it.
For a narrative comic, you'd need more characters for the world to feel convincing... unless there was a plot reason for there not to be many characters. Like if the location was somewhere isolated or there was a population depleting disaster or something.
It's like sitcoms vs other shows. A sitcom usually has limited sets (like an apartment, a restaurant, an office) and limited characters, like one group of friends or coworkers. A show like this can focus on just a few characters but run for 100s of episodes because there doesn't need a plot that keeps progressing and heightening. That's something that can easily be done with a comic strip. An action/drama show (the Flash, Buffy, Riverdale, etc) might start out with a core cast of three or so... but as the plot moves forward and progresses it'll need to add more characters for the world to feel realistic and engaging. Characters that start out as minor characters might work their way into the main cast. Like the Flash started out with 4 main characters working together and now there are like 9 or 10 people on the team at any given time fluctuating as some characters become more important or less important. In my experience that's been what long form webcomics are like.
Anyway, I'd say don't try to develop too many characters at the beginning. Start with 3 mains and see how it goes, introducing new characters as the comic goes on and the plot calls for it.